When, for example, a semiconductor component or a flat panel display is manufactured, a substrate liquid processing apparatus is used to perform a liquid processing on a substrate such as a semiconductor wafer or a liquid crystal substrate using a processing liquid such as an etching liquid.
For example, a substrate liquid processing apparatus disclosed in Japanese Patent Laid-Open Publication No. 2013-093478 performs a process of immersing a substrate in a processing liquid (an etching liquid: a phosphoric acid aqueous solution) stored in a processing bath, and etching a silicon nitride film formed on the surface of the substrate.
Meanwhile, in the conventional art, the phosphoric acid aqueous solution used as a processing liquid contains silicon which has been eluted by the etching process, and the used phosphoric acid aqueous solution is sent to a recycling unit and the silicon contained in the phosphoric acid aqueous solution is removed. In this manner, the used phosphoric acid aqueous solution is recycled by removing the silicon in the recycling unit, and is returned to the processing bath again to be used again.
However, the used phosphoric acid aqueous solution has conventionally been sent to the recycling unit, regardless of the silicon concentration.
When a phosphoric acid aqueous solution from which silicon cannot be removed, or a phosphoric acid aqueous solution from which it takes time to remove silicon is sent to the recycling unit, crystals are generated within the recycling unit or a pipe line, or a trouble occurs in an internal structure of the recycling unit.